Measurement of mechanical properties of microscale samples of material, such as thin films, is very difficult due to the small size of the material. The material properties of small structures and thin films cannot be easily related to the properties of bulk samples because of several reasons. Samples used for bulk mechanical testing generally have dimensions significantly greater than microstructural features, whereas in thin films, the geometrical and microstructural dimensions are on the same order of magnitude. Therefore, assumption of homogeneity and isotropy is not valid when obtaining the mechanical properties. Furthermore, different manufacturing techniques are used in fabricating small specimens and thin films resulting in different microstructure than bulk materials. In addition, because of comparable size of the structural dimensions and microstructural and defect dimensions, inelastic deformation mechanisms are far different from bulk specimens.
Testing materials at scales smaller than a millimeter is a challenge due to limiting factors such as specimen gripping techniques, the application of small forces, and the ability to measure small strain values. Therefore, conventional instruments cannot be used to test these properties. A challenge for creating new microscale testing systems is the design of reliable loading and data capture methods. Regular strain gages are not applicable due to their large size, and strain measurement techniques such as capacitive gages and digital image correlation are either expensive, hard to use, or not accurate enough. In addition, digital imaging correlation is a slow and labor intensive process that is not practical for long term fatigue tests.
The Measurement of mechanical properties of micro-scale samples is particularly challenging in fatigue testing of materials since load and displacement are both needed to be monitored for many cycles. The present invention is a device and method that addresses the need for applying load and measuring deformation at small scale as well as long term fatigue testing and reliable strain measurements on micro-scale samples.